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| Department
of Microbiology and Immunology University of North Dakota School of Medicine & Health Sciences 501 N. Columbia Rd Grand Forks, ND 58202 Phone: (701) 777-2214 FAX: (701) 777-2054 |
©2008
University of North Dakota |
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My
primary research interest is the structure, biochemistry
and genetic regulation of bacterial peptidoglycan, and
its importance in determining cell shape and influencing
cell division. In E. coli there are twelve known penicillin
binding proteins (PBPs), which are responsible for the
polymerization and maturation of the rigid peptidoglycan
portion of the cell wall. They are also the targets
for the beta-lactam antibiotics, one of our most important
classes of antimicrobial agents. Four "high molecular
mass" PBPs (1a, 1b, 2, and 3) are involved in the
primary elongation and septation of the wall. Another
seven are known as "low molecular mass" PBPs
and, until recently, no physiological function could
be assigned to any one of these enzymes. We are especially
interested in defining the functions of these proteins
for which we have so little information. To discover
possible functions for the LMW PBPs, we constructed
over 300 E. 
coli
mutants from which we deleted the PBPs in as many combinations
as possible. We screened these mutants for a variety
of phenotypes in which the cell wall may play a part
(including transformation, conjugation, phage sensitivity,
protein secretion, antibiotic sensitivity, and morphological
variation). Certain multiply mutated strains lacking
PBP 5 were unable to form normally shaped cells. Instead
of being simple rods of uniform shape, the mutant cells
had altered diameters and were branched or misshapen
in a variety of significant ways. So far, we have been
able to show that cell shape depends on the enzymology
activity of PBP 5 and that at least two other PBPs (4
and 7) play some sort of backup role in maintaining
normal shape.By continuing to study this large set of
mutants we hope to discover the reason E. coli and other
bacteria maintain this multiplicity of (seemingly) unnecessary
enzymes. The discoveries of new PBPs and a variety of
phenotypes suggest that cell wall metabolism is more
complicated than is usually believed.
We
have identified three genes, slyD, fkpA, and fklB that
encode prokaryotic members of the class of FK506-binding
proteins (FKBPs), which are peptidyl-prolyl cis-trans
isomerases. The predicted sequences of the FkpA and
FklB proteins are highly similar to the Mip proteins
that contribute to the ability of Legionella and Chlamydia
to survive the intracellular defenses of macrophages.
We find that the fkpA homologue in S. typhimurium also
contributes to the intracellular survival of this Gram
negative pathogen. Therefore, for basic and medical
reasons, we maintain a mutational study of the function
of the FKBPs in these bacteria.